1. Field of the Invention
The present invention relates to an apparatus for removing bubbles from a liquid having a medical use. More particularly, the invention is concerned with an apparatus for removing bubbles from a liquid such as blood flowing in an extracorporeal blood circuit of artificial organs, e.g., an artificial lung, artificial kidney, separator for separating blood plasma from blood cells, and so forth, and the dialysate which flows in a dialysis circuit in an artificial kidney.
2. Description of the Prior Art
There are three types of apparatus for removing bubbles from a liquid. These are an apparatus of filtration type, an apparatus of settling type, and an apparatus which makes combined use of both the filtration type and settling type.
The apparatus of filtration type usually employs a filter having a pore size of 20 to 45 microns or a screen having a mesh size of 180 to 200 microns. The filter, however, produces a large pressure loss and tends to damage the constituents of blood, while the screen often fails, inconveniently, to trap minute bubbles.
In the apparatus of the settling type, as well as the apparatus which simultaneously uses both the filtration type and settling type, a blood reservoir of a large volume is employed, in which the blood is temporarily stored to allow the bubbles to be separated by buoyancy. In such apparatus, it is possible to remove fine bubbles to some extent, provided that the volume of the reservoir is sufficiently large. The large reservoir volume, however, increases the quantity of blood for priming, i.e., for filling up the reservoir. Consequently, the quantity of blood or other similar liquid for transfusion, as well as the quantity of residual blood or liquid after circulation, is increased. This results in various troubles.
Under these circumstances, there has already been proposed, in the specification of Japanese Provisional Patent Publication No. 58-163372, an apparatus for use in a blood circuit which is capable of removing even fine bubbles from the blood, while diminishing the quantity of blood required for priming and minimizing the pressure loss caused by the filter. More specifically, this proposed apparatus has, as shown in FIG. 1, a vessel 2, a planar filtration member 3 disposed in the vessel 2 so as to divide the space in the vessel 2 into an upper space and a lower space, a liquid inlet port 4 provided in the wall of the vessel 2 for communication with the upper space and adapted to introduce the liquid into the upper space in the form of a vortex flow around the axis of the vessel 2, a liquid outlet port 5 provided in the wall of the vessel 2 for communication with the lower space in the vessel 2 and adapted to allow the treated blood passed through the filtration member 3 to be discharged therethrough, and a gas outlet port 6 provided in the wall of the vessel 2 for communication with the uppermost region of the upper space in the vessel 2 and adapted to allow the separated gas to be discharged therethrough. With this apparatus 1, therefore, the bubbles in the blood are positively separated centrifugally in the outer peripheral region where the velocity of vortex flow is high, while in the central region where the flow velocity is small, the centrifugally separated bubbles are allowed to float so as to be discharged through the gas outlet port. Consequently, it is possible to efficiently remove the bubbles with reduced quantity of liquid for priming.
This apparatus 1, however, suffers from the following disadvantage. Namely, the filtration member 3 having a planar shape offers substantial resistance to the blood flowing therethrough causing problems such as a pressure loss and damage to the blood. To avoid these problems, the filtration member 3 is required to have a diameter, i.e., filtration area, large enough to suppress the pressure loss and the damage to blood. Consequently, the volume of the vessel 2 is increased to require a certain quantity of blood for priming. Thus, there is still a demand for reduction of the quantity of blood for priming.
The apparatus for removing bubbles from liquid, to which the invention pertains, is used not only in the blood circuit but also in the dialysis liquid circuit of an artificial kidney for removing bubbles from the dialysis liquid. Removal of bubbles from the dialysis liquid is necessary because bubbles attaching to the dialysis membrane (wall of hollow fibers) form a dead space, thus lowering the dialysis efficiency, and may enter the human body through any defects in the wall of the hollow fiber.